Fluid energy machine, method for generating a fluid volume flow and/or for compressing a fluid and method for refuelling a vehicle

ABSTRACT

The invention relates to a fluid energy machine and a method for generating a fluid-volume flow and for compressing a fluid by means of the fluid energy machine according to the invention. The invention also relates to a method for refuelling a vehicle with a fluid using the method according to the invention for generating a fluid-volume flow and for compressing a fluid, and to the use of a fluid energy machine according to the invention for refuelling a motor vehicle. The fluid energy machine comprises a crank drive ( 20 ) and a drive device ( 10 ) that is mechanically connected to the crank drive ( 20 ), by means of which drive device a torque can be introduced into the crank drive ( 20 ), as well as a piston-cylinder unit ( 30 ), the piston ( 32 ) of which is mechanically connected to the crank drive ( 20 ). The drive device ( 10 ) comprises two electric motors ( 50, 60 ), the respective output members ( 51, 61 ) of which are mechanically connected to the crank drive ( 20 ).

The present invention relates to a fluid energy machine and a method for generating a fluid volume flow and for compressing a fluid by means of the fluid energy machine according to the invention. In addition, the present invention relates to a method for refuelling a vehicle with a fluid by applying the method according to the invention for generating a fluid volume flow and for compressing a fluid, and to the use of a fluid energy machine according to the invention for refuelling a motor vehicle.

For refuelling devices such as motor vehicles with hydrogen, which may be present in liquid form, so-called cryo-pumps are known that are suitable for pumping a fluid in the low-temperature range.

DE 102007 035616 A1 discloses a pump which is designed in particular for cryogenic media. This pump comprises a piston-cylinder assembly that is set up to pump and/or compress very cold fluids, such as hydrogen.

Pumps of this type are usually operated with a hydraulic drive. Instead of the hydraulic drive, other conventional low-temperature pumping devices comprise a rotary drive, wherein in this case, a proven approach in particular is to connect an electric motor to a crank drive, which in turn is coupled to the piston of the piston-cylinder assembly.

The hydraulic drive for the low-temperature pumping device typically requires a relatively large installation space to accommodate additional components, as well as a cooling system and a reservoir for the hydraulic fluid. In addition, in terms of installation and maintenance a pumping device with hydraulic drive, together with the associated measuring equipment to be installed for distance measurement in the hydraulic cylinder, is relatively expensive. This usually requires a linear distance-measuring system to be arranged. To prevent impermissible peak values of the volume flow from being generated, a sinusoidal-like acceleration curve of the piston must be set in the pumping device. When using a hydraulic drive device, the implementation of a corresponding acceleration curve is associated with increased complexity with regard to the control operations required and the control equipment that must be installed to provide them. In addition, when using hydraulic drive devices it is typically impossible to generate strokes of the piston-cylinder unit with a frequency of more than approximately 2 Hz.

In the design variant with an electromotive drive in combination with a crank drive, the maximum frequency-dependent nominal torques of standard commercial electric motors limit the maximum pumping capacity of the pumping device with regard to the achievable flow rate and the achievable pumping pressure. When a high flow rate and high pressure are sought, corresponding frequencies of the stroke movements, in addition to forces or moments, must be applied to the crank drive by the electric motor. This means that corresponding counter-forces act on the electric motor or its mounting and/or the mounting of a torque-transmitting machine element between the electric motor and the crank drive. The stability of the bearing sites must be adapted to this if they are not to be exposed to the resulting wear, which is especially noticeable if the output member of the electric motor is arranged substantially coaxially to the axis of rotation of the crank drive and is fixedly connected to this crank drive.

The object of the invention therefore is to provide a fluid energy machine and a method for generating a fluid volume flow and/or for compressing a fluid, with which a fluid, such as gaseous hydrogen, can be compressed and a fluid, which here can be either gaseous or liquid hydrogen, can be pumped in a simple, cost-effective and reliable way that requires low maintenance. Other aspects of the object addressed by the invention are to provide a method for refuelling a vehicle with a fluid, and a use of the fluid energy machine according to the invention.

To achieve this object, a fluid energy machine according to claim 1 and a method for generating a fluid volume flow and/or for compressing a fluid according to claim 9 are provided. Advantageous configurations of the fluid energy machine according to the invention are specified in the dependent claims 1 to 8.

The fluid energy machine according to the invention comprises a crank drive and a drive device which is mechanically connected to the crank drive, with which a torque can be introduced into the crank drive. Furthermore, the fluid energy machine comprises a piston-cylinder assembly, the piston of which is mechanically connected to the crank drive. It is provided according to the invention that the drive device comprises two electric motors, whose respective output members are mechanically connected to the crank drive. It is further provided that the piston-cylinder assembly comprises only one piston and only one cylinder. The electric motors, hereafter also abbreviated to motors, are rotary motors, while the possibility of the arrangement of more than two motors is also not excluded. The drive device the comprises at least two motors. The torques of these motors, or of the drive device, are applied to the crank drive, in particular to the crank thereof, in order to actuate the crank drive and implement a displacement of the piston of the piston-cylinder unit. The torque of each motor is extracted from the output member thereof, for example from its shaft journals. The mechanical connection of the piston to the crank drive is implemented by the fact that the piston is mechanically connected to the connecting rod or coupling of the crank drive.

The crank drive preferably comprises only one crank and a coupling or connecting rod connected thereto, wherein the at least two motors arranged according to the invention apply their respective torque to this one crank.

In an alternative design, two parallel cranks and couplings are present, so that each of the two motors acts on one crank drive each. The crank drives are connected to the piston.

The fluid energy machine according to the invention is a low-temperature pump for generating a fluid volume flow and for compressing a fluid. With this pump or compressor, it is possible to generate a volume flow of liquid or gaseous hydrogen and to implement the compression of gaseous hydrogen. In one configuration according to the invention the fluid energy machine is set up such that the fluid can be compressed up to a pressure of 50 to 1000 bar, in particular up to 350 to 500 bar or 700 bar.

Preferably, all motors arranged according to the invention are electric motors, but the application of hydraulic motors as well is not intended to be excluded.

The mechanical connection of the motors to the crank drive is preferably implemented on the crank of the crank drive, so that the particular motor torque is introduced into the crank. This crank can also be configured as an eccentric disc. The mechanical connection of the two motors to the crank can be implemented in particular on both sides of the plane of motion of the crank of the crank drive, for example by means of two parallel-mounted eccentric discs, which each form a crank and which are connected to a coupling or a connecting rod. In this arrangement, shafts are arranged coaxially between the motors and the crank drive for transmitting the torque.

An advantage of the fluid energy machine according to the invention is that it operates despite slow rotation speeds of the shaft from 1 to 600 revolutions per minute (rpm), and yet it can still generate the necessary high pressures. In spite of the slow rotation speeds, by using the electric motors a high torque in the range of 1000 to 4000 Nm can be achieved. The resulting force exerted on the piston rod is in the range of 20 to 15 kN.

In a first design variant of the fluid energy machine according to the invention, the output member of at least one electric motor is directly connected by means of a shaft to the crank of the crank drive. This means that, for example, the motor journal of one motor is connected to a shaft that is directly mechanically connected to the crank.

In a further design variant of the fluid energy machine according to the invention, it is provided that between one output member of at least one electric motor and the crank of the crank drive a transmission, in particular a helical gearbox, is arranged for transforming the torque generated by the electric motor up or down. In this design variant a symmetrical arrangement is preferred, so that both motors are connected to one transmission each, which in turn is connected to the crank drive. The crank drive preferably comprises two drive shafts, so that in each case a transmission is arranged between a motor and a drive shaft. This is not intended to exclude the design of the invention in which one of the motors is directly mechanically connected to the crank drive and the other, or additional motor is connected to the crank drive indirectly, namely via a transmission.

The crank drive should preferably comprise a connecting rod which is connected to the piston of the piston-cylinder unit mechanically, for example via a joint. This connecting rod, also designated as a coupling, is preferably connected in a rotary articulated fashion to the piston and in a rotary articulated fashion to the crank.

Connecting two motors to the crank drive results in a symmetrical load and a distribution of the counter-forces or counter-moments over the two motors or their drive shafts, which enables the load and/or wear on the drive device or the crank drive overall to be reduced.

The bearings can be dimensioned correspondingly smaller, or the shafts can be designed with a smaller diameter.

In a preferred design of the fluid energy machine, the shaft is mounted on a ball bearing. This is facilitated in part by the low rotation speeds. The entire fluid energy machine has a relatively low volume requirement.

In addition, conventional commercial electric motors with a comparably low rated torque or low rotation speed can also be used to implement the higher pressure and throughput rates, such as are required, for example, at a hydrogen filling station.

In the method for using a fluid energy machine according to the invention for generating a hydrogen volume flow and compressing hydrogen, the hydrogen which is to be transported and compressed is provided in a liquid state, wherein the hydrogen is fed to the piston-cylinder unit and the electric motors of the fluid energy machine are operated so that the piston of the piston-cylinder unit is displaced and a hydrogen volume flow is thereby generated and the hydrogen is compressed.

The method according to the invention is advantageously used for refuelling a vehicle with liquid or gaseous hydrogen. Either liquefied hydrogen in pumped into a vehicle to be refuelled, in which case only a volume flow is generated, or else gaseous hydrogen is pumped, in which configuration of the method a volume flow is generated and the gas is also compressed at the same time.

The fluid energy machine is preferably designed as a two-stage piston machine and in the first stage, a pre-compression of the hydrogen takes place and in the second stage the compression up to the system pressure takes place. During the pre-compression stage the pressure is advantageously increased by from 4 to 12 bar. The system pressure is preferably between 50 and 1000 bar, in particular between 350 and 500 bar.

The two stages are designed such that the pre-compression or pre-charging occurs when the piston is being moved upwards, i.e. in the direction of the drive device. During the downward movement of the piston, i.e. when the piston moves in the direction of the outlet device, the pressure increases from the initial pressure of the first stage up to the system pressure. The system pressure is limited by the maximum pump output pressure.

In a method according to the invention for using the fluid energy machine described, the pumping quantity of hydrogen of the fluid energy machine is adjusted via the frequency of the electric motors and this is between 0 and 250 kg/h, and in particular between 30 to 200 kg/h.

The invention is described in the following by reference to the exemplary embodiments shown in the accompanying drawings.

Shown are

FIG. 1: a fluid energy machine according to the invention in a first embodiment,

FIG. 2: a fluid energy machine according to the invention in a second embodiment.

The embodiments shown in FIGS. 1 and 2 differ in that in the version shown in FIG. 1, the motors are directly connected to the crank drive and in variant 2 shown in FIG. 2, transmissions are provided between the motors and the crank drive.

To describe the features present in both embodiments, reference will be first made to both figures.

Both versions comprise a drive device 10, which in the exemplary embodiments shown is implemented by a first motor 50 and a second motor 60. Both motors are implemented as electric motors. Both motors 50, 60 are each connected to a rotation rate sensor 53, 63 for setting the motor rotation speed. In both embodiments of the fluid energy machine a crank drive 20 is provided, which comprises a crank 21, shown here with two eccentric disks, and a connecting rod 22 or coupling, which is connected to the crank 21 or to the two eccentric disks thereof via a first joint 23. Furthermore, in both embodiments a piston-cylinder assembly 30 is provided, which comprises a piston 32 that can be displaced in a cylinder 31. The connecting rod 22 or coupling of the crank drive 20 is connected via a second joint 24 to the piston 32 of the piston-cylinder assembly 30. During rotation of the crank 21, a typical combined motion of rotation and translation of the connecting rod 22 takes place, which absorb the shear forces from the piston 32, the piston rod of which is mounted on both sides by bearings, not shown here, which each form a sliding joint, and cause the forced operation of the piston 32 in the cylinder 31 in the form of a piston stroke action.

On the cylinder 31 of the piston-cylinder assembly 30 an inlet device 33 is provided for feeding a fluid 40 into the cylinder 31, and an outlet device 34 for discharging the fluid 40 located in the cylinder 31, which may be compressed. The first motor 50 comprises a first output member 51 and the second motor 60 comprises a second output member 61. These output members 51, 61 are, for example, the shaft journals of the motors 50, 60. The respective output member 50, 60 is connected to a shaft, so that the first output member 51 is connected to a first shaft 52 and the second output member 61 is connected to a second shaft 62.

In the embodiment shown in FIG. 1 both the first shaft 52 and the second shaft 62 are connected directly to the crank 21 of the crank drive 20, so that a torque generated by the respective motor 50, 60 is applied via the output member 51, 61 to the shaft 32, 62 arranged thereon and by this shaft 52, 62 is applied to the crank 21 of the crank drive 20, so that the stroke motion of the piston 32 can be implemented by the crank drive 20.

In the embodiment shown in FIG. 2 the first shaft 52 is connected to a first transmission 70, which comprises a first driving spur gear 71 on the first shaft 52, which gear meshes with a first driven spur gear 72 that is seated on a first output shaft 73, which is rigidly connected to the crank 21 of the crank drive 20.

In a similar manner, a second driving spur gear 81 sits on the second shaft 62, which gear meshes with a second driven spur gear 82, which in turn is seated on a second output shaft 33 that is rigidly connected to the crank 21 of the crank drive 20. This mechanism allows the torque and the rotation speed of the motors 50, 60 to be transformed up or down, to increase the torque to be generated by the crank drive 20 or else to increase the frequency of the motion of the piston 32.

The invention is not limited to an embodiment shown in FIG. 2 with a symmetrical arrangement of transmission members, rather it can also be provided to arrange different transmissions between the motors 50, 60 and the crank drive 20 and possibly also couplings between the respective motor 50, 60 and the crank drive 20, in order to engage or disengage a drive train as appropriate and thereby provide a torque on demand.

LIST OF REFERENCE NUMERALS

-   Drive device 10 -   Crank drive 20 -   Crank 21 -   Connecting rod 22 -   First joint 23 -   Second joint 24 -   Piston-cylinder unit 30 -   Cylinder 31 -   Piston 32 -   Inlet device 33 -   Outlet device 34 -   Fluid 40 -   First motor 50 -   First output member 51 -   First shaft 52 -   First rotation rate sensor 53 -   Second motor 60 -   Second output member 61 -   Second shaft 62 -   Second rotation rate sensor 63 -   First transmission 70 -   First driving spur gear 71 -   First driven spur gear 72 -   First output shaft 73 -   Second transmission 80 -   Second driving spur gear 81 -   Second driven spur gear 82 -   Second output shaft 83 

1. A fluid energy machine, comprising a crank drive and a drive device which is mechanically connected to the crank drive, with which a torque can be introduced into the crank drive, and also comprising a piston-cylinder assembly, the piston of which is mechanically connected to the crank drive, characterized in that the drive device comprises two electric motors, the respective output members of which are mechanically connected to the crank drive and that the piston-cylinder unit comprises only one piston and only one cylinder.
 2. The fluid energy machine according to claim 1, characterized in that the fluid energy machine is a low-temperature pump, for generating a fluid volume flow and for compressing a fluid.
 3. The fluid energy machine according to claim 1, characterized in that the fluid energy machine is set up such that the fluid can be compressed up to a pressure of 50 to 1000 bar.
 4. The fluid energy machine according claim 1, characterized in that the mechanical coupling of the electric motors to the crank drive on the crank of the crank drive is implemented such that the motor torque is introduced into the crank.
 5. The fluid energy machine according to claim 4, characterized in that an output member of at least one electric motor is directly coupled to the crank of the crank drive by means of a shaft.
 6. The fluid energy machine according to claim 4, characterized in that between an output member of at least one electric motor and the crank of the crank drive a transmission is arranged for transforming the torque generated by the electric motor up or down.
 7. The fluid energy machine according to claim 1, characterized in that the crank drive comprises a connecting rod, and the piston is mechanically connected to the connecting rod.
 8. The fluid energy machine according to claim 1, characterized in that the shaft is mounted on a ball bearing.
 9. A method for using a fluid energy machine comprising a crank drive and a drive device which is mechanically connected to the crank drive, with which a torque can be introduced into the crank drive, and also comprising a piston-cylinder assembly, the piston of which is mechanically connected to the crank drive, characterized in that the drive device comprises two electric motors, the respective output members of which are mechanically connected to the crank drive and that the piston-cylinder unit comprises only one piston and only one cylinder for generating a hydrogen volume flow and for compressing hydrogen, said hydrogen to be transported and compressed being provided in a liquid state, characterized in that the hydrogen is fed to the piston cylinder assembly and the electric motors of the fluid energy machine are operated such that the piston of the piston cylinder assembly is displaced and a hydrogen volume flow is thereby generated and the hydrogen is compressed.
 10. The method according to claim 9, characterized in that the compressed hydrogen is used for refuelling a vehicle with liquid or gaseous hydrogen.
 11. The method according to claim 9, characterized in that the fluid energy machine is designed as a two-stage piston machine and in the first stage a pre-compression of the hydrogen takes place and in the second stage the compression up to the system pressure takes place.
 12. The method according to claim 11, characterized in that during the pre-compression the pressure is increased by from 4 to 12 bar.
 13. The method according to claim 11, characterized in that the system pressure is 50 to 1000 bar.
 14. The method according to claim 9, characterized in that the pumping quantity of hydrogen of the fluid energy machine is adjusted via the frequency of the electric motors and this is between 0 and 250 kg/h.
 15. The method as claimed in claim 13 characterized in that the system pressure is 350 to 700 bar.
 16. The method as claimed in claim 13 characterized in that the system pressure is 350 to 500 bar.
 17. The method as claimed in claim 14 characterized in that the pumping quantity of hydrogen is between 30 to 200 kg/h. 